Metabolites of arachidonic acid play an important role as modulators or mediators of vascular tone and platelet aggregability. PGI2 is the principal prostaglandin produced by the endothelial cell whereas the platelet synthesizes mainly TxA2. However, arachidonic acid may also be metabolized by the lipoxygenase pathway to hydroperoxy-, hydroxy, and dihydroxy-eicosatetraenoic acids (HPETE, HETE, and DIHETE) as well as leukotrienes. The proposed studies will test the hypothesis that a metabolite or metabolites of arachidonic acid are involved in the regulation of these pathophysiological changes in the coronary vasculature and in the platelet and contribute to myocardial ischemia and injury. We will develop two animal models of coronary atherosclerosis and identify the arachidonic acid metabolites synthesized by the coronary endothelium. Then the role of these metabolites will be tested in vivo in the two animal models. In one model, a focal arteriosclerosis will be produced in dogs by mechanical injury and hyper-cholesterolemia. The second model will be the Watanabe Heritable Hyperlipidemic (WHHL) rabbit. These rabbits have a genetic deficiency of their low density lipoprotein (LDL) receptors and develop a progressive atherosclerosis. In these models, angiography and morphological techniques will be used to characterize the natural history of the arteriosclerotic lesions, and pharmacologic methods will be used to determine changes in vascular reactivity during progression of the disease. To study the metabolism of arachidonic acid, human and bovine coronary artery endothelial cells will be grown in tissue culture. Initially, the metabolism of arachidonic acid by the cyclooxygenase pathway will be investigated, and the major prostagladins identified. Studies will be designed to identify the HETE's and diHETE's formed by the lipoxygenase(s) of the endothelial cell. Special attention will be given to the 5-lipoxygenase, the initial step in the synthesis of leukotrienes. Following the identification of the arachidonic acid metabolites, studies will be designed to identify factors that stimulate or inhibit their synthesis. The physiological effects of the metabolites on platelet aggregability and vascular tone will be determined in vitro and in vivo in the two animal models. Assays will be developed for the metabolites and used to characterize the release in vitro from cells and in vivo in the two animal models.